EFFECT OF CONDUCTIVE SUBSTRATE ON DISSOLUTION AND LATERAL DIFFUSION OF METALS IN VITREOUS CHALCOGENIDES

It is shown that metallic substrates strongly influence the dissolution and lateral diffusion of silver and zinc into amorphous chalcogenides. Very large amounts of metals can be dissolved in chalcogenide films with the excess of the metal deposited on the conducting substrate provided the electronegativity of the latter is higher than that of the dissolving metal. Lateral diffusion is shown to proceed much faster if the chalcogenide film is evaporated on to a conductive coating of gold or nickel and more slowly in the case of aluminium or an oxide glass, the lateral diffusion rate being independent of the conductivity of the substrate. The effect of the conducting substrate is more pronounced in the case of thermal diffusion than in the case of photodiffusion. A microscopic model for the dissolution/diffusion process is proposed based on the assumption that the metal/doped chalcogenide boundary is actually an electrode/solid electrolyte contact and the doped/undoped chalcogenide interface is to be regarded as a semiconductor heterojunction.